A location-determining receiver, such as a Global Positioning System (GPS) receiver or a GLONASS (Global Navigation Satellite System) receiver, estimates the position, attitude (e.g., tilt, roll, or yaw), or both of an object or a vehicle. The location-determining receiver may experience imprecise pseudo-range and carrier phase measurements, where the location-determining receiver receives (e.g., transiently) one or more satellite signals of low signal strength or poor signal quality.
GLONASS (Global Navigation Satellite System) and GPS use different satellite constellations and different modulation schemes for their respective satellite transmissions. The GLONASS constellation includes over twenty satellites and broadcasts signals over different frequencies in accordance with a frequency division multiple access (FDMA) modulation and a frequency reuse plan, whereas the GPS system uses spread spectrum modulation or code division multiple access modulation (CDMA) where the transmission frequencies are generally the same for each satellite. Because the GLONASS satellites transmit on different frequencies, which may lead to differences in propagation through the ionosphere or troposphere or other errors, the GLONASS location-determining receiver is susceptible to position error from inter-channel bias associated with the different transmission frequencies of satellites.
Certain location-determining receivers may use an error-reduction filter (e.g., Kalman filter) to filter the results of carrier phase measurements or processed carrier phase measurement data, for example. Some location-determining receivers may use a Receiver Autonomous Integrity Monitoring (RAIM) technique to detect errors of analyzed pseudo-range measurements by comparing the analyzed pseudo-range measurements to reference pseudo-range measurements, where erroneous or outlying pseudo-range measurements can be excluded from a position or attitude solution to improve accuracy of the estimated position or attitude of the object or the vehicle. Neither the error-reduction filter approach, nor the RAIM technique fully addresses the aforementioned problem of imprecise pseudo-range and carrier phase measurements, where the location-determining receiver receives (e.g., transiently) one or more satellite signals of low signal strength or poor signal quality. Thus, there is a need for a location-determining receiver that is capable of using both GPS and GLONASS transmission signals to increase accuracy of position and attitude estimates in real time, while compensating for bias error.